Ruth's is a delightful surprise. It is in the style of a trattoria, that is, the printed menu is not extensive, and not a reliable guide to what they are offering on any given day. Roughly, they offer pasta, pizza, fish and falafel, but to say so fails to do justice to the quality of the kitchen. The fish (2 or 3 types on any day, but the type depends on what is in the market that day) is cooked perfectly. You can have it grilled or simmered (perfectly) in whatever version of a vegetable couscous that they are cooking that day (again, depending on what vegetables are fresh in the market) Or you can have the couscous as a vegan main course. You can ask for the couscous (and other dishes) to be spiced very lightly, or hot enough for a Tunisian. They do a fabulous artichokes (a traditional Italian Jewish dish) when artichokes are in season, but you have to know to order it. The pasta sauces available will also vary according to what looks good in the market. Heavily patronized by locals, although tourists come and you will dine with all of the other Yidden in Florence for your convention.
You get fresh, delicious home-cooking style meals in the best tradition of the trattoria. The Tuscan bread and pita are baked on premises. They pour a excellent local wines. The owner, Simcha, is something of a character; do consult with him over your choice of wine and food. They grate excellent Romano over your perfectly cooked pasta.
Best to read the menu b'Ivrit: Boreka for example) is translated as "brick" in English and Italian. Order the cheese borekas. Also order the cheese crepes for dessert, a soft, white, cinnamon-infused cheese filling, not overly sweet) I had lunch and dinner from Ruth's ever day for a week, so I got to try everything.
They will send delicious meals to your hotel. Or pack up bread, hummus, and other portable things for you to take away. They sell a few items (wine, cheese) since Florence has no kosher shop. Open on Shabbat only if sufficient people make reservations (or at the whim of the owner), but will send challah, wine and a delicious Shabbos meals to your hotel.